The present invention relates to a thermal actuator for a micro electro-mechanical device. The invention is herein described in the context of an ink jet printer but it will be appreciated that the invention does have application to other micro electro-mechanical devices such as micro electro-mechanical pumps.
Micro electro-mechanical devices are becoming increasingly well known and normally are constructed by the employment of semi-conductor fabrication techniques. For a review of micro-mechanical devices consideration may be given to the article xe2x80x9cThe Broad Sweep of Integrated Micro Systemsxe2x80x9d by S. Tom Picraux and Paul J. McWhorter published December 1998 in IEEE Spectrum at pages 24 to 33.
One type of micro electro-mechanical device is the ink jet printing device from which ink is ejected by way of an ink ejection nozzle chamber. Many forms of the ink jet printing device are known. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
A new form of ink jet printing has recently been developed by the present applicant, this being referred to as Micro Electro Mechanical Inkjet (MEMJET) technology. In one embodiment of the MEMJET technology, ink is ejected from an ink ejection nozzle chamber by a paddle or plunger which is moved toward an ejection nozzle of the chamber by an electro-mechanical actuator for ejecting drops of ink from the ejection nozzle chamber.
The present invention relates to a thermal actuator for use in the MEMJET technology and in other micro electro-mechanical devices.
The invention is defined broadly as providing a thermal actuator for a micro electro-mechanical device. The actuator comprises a first conductive material arm which is attached at one end to a substrate and which, at its other end, is connected to or integrated with a movable element. The first arm is arranged, in use, to be heated by passage of electrical current and the first arm is formed along its length with a profile that functions to concentrate heating in the arm to a region adjacent the attachment to the substrate. The thermal actuator preferably includes a second arm which extends between the substrate and the movable element and which is arranged such that, when the first arm is heated, the first arm is caused to expand relative to the second arm and exert a deflecting force on the movable element.
The second arm preferably is coupled to the first arm by a coupling means and the coupling means most preferably is located intermediate the ends of the first arm. Also, the first arm preferably is formed intermediate its ends with a thermal sink.
The present invention also provides a liquid ejector comprising a nozzle chamber, a liquid ejection aperture in one wall of the chamber, a liquid ejection paddle located within the chamber and a thermal actuator extending into the chamber by way of an access aperture in a second wall of the chamber. The thermal actuator itself comprises a first conductive material arm which is attached at one end to a substrate and which is connected at its other end to the liquid ejection paddle. The first arm is arranged, in use, to be heated by passage of electrical current and the first arm is formed along its length with a profile that functions to concentrate heating of the arm adjacent its attachment to the substrate. In use of the ejector, when the first arm is heated the liquid ejection paddle is caused to move from a first position to a second position to thereby cause ejection of liquid through the liquid ejection aperture.